[ltc8k6]

I’m sticking with what I can see. The tungsten bar does not fit exactly into the opening, so it can’t be a casting process.

I think we can see a logical progression.

They started off by drilling out the bars and inserting tungsten rods.

Then they figured out that they could hollow out the whole bar and insert a tungsten block.

[Wonder Warthog]

"I’m sticking with what I can see. The tungsten bar does not fit exactly into the opening, so it can’t be a casting process."

Those gaps could have been formed quite easily when the bar was cut open, and in fact, I would expect to see precisely what is shown as a result of such an operation. The gold will deform, the tungsten will not. The result is a "gap" between the rod and the bar.